BURBANK, Calif. - John Ritter knows why Katey Sagal is his perfect foil: "Katey's got the kind of laugh, once you hear it you'll do everything you can to hear it again."

And yes, Sagal laughs when told what Ritter, her ebullient co-star on 8 Simple Rules for Dating My Teenage Daughter (8 p.m. Tuesday, Channels 2, 9), has said about her.

She first met Ritter some years ago when they were performing at a fund-raiser in Los Angeles. "John and I got along immediately, because I'm a pretty good audience," she said.

In 1998, Sagal and Ritter co-starred in the TV movie Chance of a Lifetime, a lonely hearts romantic comedy in which Sagal wore a fat suit.

Now they're paired on the ABC sitcom, drawn from the book of the same name by W. Bruce Cameron, as Paul and Cate Hennessy, parents to teenagers Bridget (Kaley Cuoco), Kerry (Amy Davidson) and Rory (Martin Spanjers).

8 Simple Rules for Dating My Teenage Daughter, now finishing its first season, will air a two-part finale on Tuesday and May 20.

Cybill Shepherd will guest star as Cate's sister, whose visit to the Hennessy family proves rather disruptive.

Sagal, who played trashy wife Peg Bundy for 11 years on the Fox comedy Married ... With Children, says she had to "jump through hoops" to get the role of Cate Hennessy, even though it wasn't a big part as written for the pilot.

Dealing with past

"I do have my past that follows me around that says 'big red wig,"' she says. (Married ... With Children, also starring Ed O'Neill, ran from 1987-97.)

As the season progressed, Cate developed from something of a sidebar to the story of a father and his daughters into "a full person, with a point of view," Sagal said.

What's important to Sagal is that Ritter's character - a work-at-home sportswriter dad - is "not a silly, stupid father."

"He's just a naive father - caught off-guard more than anything else," she said. "So Cate's not demeaning to him. She does have a rock sensibility, but not to the detriment of everyone else."

Sagal, a single mother of two, says 8 Simple Rules is "very reality-based," which sets it apart from most other present-day family sitcoms.

The show has appeal to both children experiencing the complexity of today's lifestyle and parents who are "raising children who have no idea what's really going on with them."

Sagal, 47, grew up in Hollywood in a show-biz family. Her father was director Boris Sagal (The Omega Man, Girl Happy).

"I was going to be a rock star," she says. But her father tried to channel her into acting, giving her jobs in projects he directed, including a mental patient in the 1971 TV thriller The Failing of Raymond.

Sagal also played a secretary in a 1973 episode of the TV crime drama Columbo, but said she knew she wasn't "like a mainstream person."

When an important producer told her she'd never work in television "because you aren't blond," Sagal said she told her father, "See, this isn't going to work."

Pursued career in rock

She then went off to pursue that rock career, which included a stint as one of Bette Midler's Harlettes - "one of the more subdued ones."

However, eventually "I got pretty beaten down ... there was no glamour at a certain point in struggling," Sagal said.

She accepted an offer from friends to appear in a rock musical called Backstreet at a theater in a converted garage. An agent spotted her and "I've just been working ever since."

"It's a real testament to not having an agenda about what I'm going to do next with my life." said Sagal.